Message-ID: <4C9F2D75.6070601@gmail.com>
Date: 2010-09-26T11:24:37Z
From: Manuel Spínola
Subject: Dealing with heteroscedasticity in repeated measure models
Dear list members,
I am fitting a repeated measure model using lme.
I have 4 measurements of a rate (variable called ipa) measured each year
(variable called tempo, which was centered) on 48 counties (all the
counties from a province, variable called localidad).
I am considering county like a random factor.
My models are:
model1 = lme(ipa ~ tempo, data=ipa, random = ~1 | localidad) # random
intercept
model2 = lme(ipa ~ tempo, random = ~1 | tempo/localidad, data=ipa) #
random intercept and slope
model3 = lme(ipa ~ tempo, random = ~1 | localidad, data=ipa,
correlation=corAR1(form=~ tempo))
I have heteroscedasticity.
Is my last model dealing with heteroscedasticity?
Thank you very much in advance.
Best,
Manuel
--
Manuel Sp?nola, Ph.D.
Instituto Internacional en Conservaci?n y Manejo de Vida Silvestre
Universidad Nacional
Apartado 1350-3000
Heredia
COSTA RICA
mspinola at una.ac.cr
mspinola10 at gmail.com
Tel?fono: (506) 2277-3598
Fax: (506) 2237-7036